Outer core density heterogeneity and the discrepancy between PKP and PcP travel time observations

Abstract

We derive 3-D tomographic maps of the Earth's mantle, CMB and outer core, from seismic P, PcP, PKPbc, PKPdf travel time data, based on the bulletins of the International Seismological Centre (1964-1995), after source relocation by Antolik et al. [2001] and phase re-identification by Engdahl et al. [1998]. Maps of the CMB derived independently from core-reflected (PcP) or corerefracted (PKP) phases are not well correlated. We attempt to explain this discrepancy, and study the radial coherence of whole-Earth tomographic images, to identify possible trade-offs between CMB undulations and velocity anomalies in the mantle or outer core. Imaged velocity anomalies in the lowermost mantle are anticorrelated with the topography of the CMB; likewise, imaged lateral heterogeneities in the outer core are correlated with the topography of the CMB. This, together with the study of Piersanti et al. [2001], suggests that the core anomalies might not be entirely fictitious.